Title:
M oon-sighting satellite “Otsukim i”
Primary Point of Contact (POC) & email:
Co-authors:
Bianca Szasz; [email protected]
Nori Ait-Mohammed, Shingo Fuchikami, Akira Miyahara, Hiroshi Ishihara, Atomu Tanaka, Yuzo
Tanaka, Takahiro Tomioka, Haruka Nishio, Yoshihiro Mashima, Shiyi Chen, Halla Almubarak, Duong Bui Nam,
Taiwo Tejumola Raphael, Long Trinh Thang, Daiki Muto, Kateryna Aheieva, Mohamed Yahia Edries
Organization:
Kyushu Institute of Technology
（x）We apply for Student Prize.
1.
N eed
In Muslim countries, religious feasts depend on the Arabic monthly (Hijri) calendar that is
related to lunar phases as seen from the Earth, i.e. the Islamic calendar is a lunar calendar and
used by Muslims all over the world to determine the proper days on which to start the annual
fast (Ramadan), to attend Hajj, and to celebrate other Islamic events.
Current methods for Moon-sighting
typically employ the naked eye or telescopes,
but clouds, pollutants, and other natural
factors frequently interfere with observations,
leading to confusion or lack of knowledge
regarding appearance of the lunar crescent.
Establishment of a ground-based network of
astronomical stations to observe the Moon
would be costly project and would not solve
Figure 1:
Lunar phases
disputes already existing between different Muslim countries, as Moon-sighting would still
depend on the weather and pollution and there would be resulting arguments regarding the
lunar crescent. Sighting moon phases (Fig. 1) throughout the year could be achieved by
observing lunar phases using a dedicated satellite, and sending the data to all concerned users.
2.
M ission Objectives
The Otsukimi Mission Objectives are the following:
I. The primary mission objective will be achieved if Otsukimi can capture the lunar phase
and image at sunset and transmit the data to users within approximately 2 hours.
II. A secondary mission objective will be achieved if the countries involved can develop and
operate satellite ground stations in their respective countries to form a network.
III. A secondary mission objective will be achieved if a database of lunar images from the
satellite can unify the starting of Arabic months for numerous Muslim countries.
IV. A secondary mission objective will be achieved if the project encourages developing
countries involved in the project to embrace space technology in solving their
developmental challenges (at least 4 countries).
V. A secondary mission objective will be achieved if the project encourages universities in
the countries involved to develop nano-satellites projects, which will be based on
successful missions in other countries (e.g. Japan).
1
3.
Concept of Operations
The main satellite mission purpose is to supply
data concerning the New Moon to Muslim
communities as soon as possible and to
regularly
send
lunar
pictures
to
ground
stations for various studies. Therefore, there
will be two modes of downlink. One of these is
normal downlink mode which will be active
during every orbit and another one is the
New Moon mode. In normal mode, there
Figure 2: Otsukimi orbit and main ground station
will be data downlink to the main ground station which will be Svalbard Satellite Station, in
Norway, near the North Pole (Fig. 2). In the New Moon mode, the ground station should obtain
the New Moon data/image as soon as possible. Consequently, a ground station network spread
all over the world will be used to receive data of the New Moon. After the Moon images are
downlinked to the ground stations, they will be immediately uploaded to the Internet for
anyone to access.
4.
Key Perform ance Param eters
Here we consider the following three key performance parameters:
•
Resolution of the Moon images
•
High accuracy attitude determination
•
Communication rate
The minimum camera requirement is to capture lunar phase. The correlation between the
theoretical value of the image sensor and the focal length of the camera must be determined.
The angle of viewθ is determined from the value of Y as the distance L (distance from Earth to
the Moon) is fixed to about 350,000 km ~ 400,000 km. Focal length is chosen to be around 80
mm~260 mm and the desired resolution of the moon image is considered to be over 100 pixels.
Y：Vertical length of the photo [km]
y：Vertical length of the image sensor [mm]
L：Distance to the subject [km]
f：Focal length [mm]
θ：Angle of view [deg]
Figure 3: Camera focal length
Due to the fact that the Otsukimi satellite must constantly track the Moon, to determine its
own location and to be able to change its orientation (actuation), two ADCS modes shall be
implemented:
•
POWER mode: Power generation is the main objective (using sun sensors: FOV: 114°,
Accuracy: <0.5°);
2
•
MISSION mode: Taking the Moon picture is the main objective. A star tracker
(accuracy: 18 arcsec (x,y axis) 122 arcsec (z axis)), reaction wheels (momentum Storage:
7.6 mNms at 1000 rpm, maximum Torque: 0.625 mNm) and magnetorquers (3 axes,
actuation level 0.24 Am² max) will be used.
For downloading the mission data to the ground, for transmitting beacon and telemetry and for
uplinking commands from the ground stations, the following drivers are chosen for the
Communication subsystem:
•
Visibility window for communication with ground segment: for orbit of altitude ~ 1000
km, the visibility window that makes the connection between the satellite downlink /
uplink possible is around 10 minutes;
•
Mission data size: mission data size is 10 MB maximum (as determined by the Camera
system) and the data rate is 1Mbps which allow transmitting the mission data of 10MB
in 80 Seconds;
•
Frequencies: an S-band transmitter will send mission data. Telemetry shall be
transmitted via UHF and commands uplinked from the ground station via VHF.
5.
5.1
Space Segm ent Description
Cam era: It was first necessary to determine the desired resolution of the Moon. The
method to determine the desired resolution of the Moon ( n [pxl], the image comparison of 25
[pxl] ~ 800 [pxl] ) is shown in Fig. 4, where the desired resolution of the Moon is at least 100
[pxl]. To determine the vertical length of the photo as N[pxl], we used the ratio n/N from the
graph shown in Fig. 5. Choosing the Moon image as 100 [pxl] ~ 300 [pxl], a 1/4 moon size and
VGA resolution camera is adequate. Choosing the QXGA resolution camera is sharpest, but as
there are constraints on image data size, a lower resolution is necessary. These calculations
and constraints led to the choice of the camera model CV-M9 GE from JAI Camera Solutions.
Figure 4:
5.2
Moon images at pixel sizes
Figure 5:
Moon size/Height of Photo
Attitude Determ ination and Control Sub-system (ADCS):
The Otsukimi
satellite will constantly track the Moon using a 3-axis controlled ADCS. The camera will be
operated during 20% of any given orbit and the COM subsystem during 10% of the orbit. It is
3
possible to determine the ratio between the angular velocity of the satellite and the angular
velocity of the Moon around the Earth. This ratio will determine the angular velocity regarding
the satellite inertial frame and this data will be provided by the Otsukimi inner actuator
(reaction wheels, magnetorquers). In case the satellite direction is lost, it is possible to obtain
an initial vector (i.e. Earth/Vernal Equinox vector) to reset the tracking process. Also, the
Otsukimi camera shall not be flooded with sunlight during operation so it is necessary to find a
trade-off between power generation and mission operation.
5.3
Com m unication subsystem (COM ): The system has two operational modes:
transmitting mode and normal mode. In the transmitting mode COM is transmitting mission
data through the S-band transceiver or uplinking commands when communicating with the
ground station. The normal mode is when the COM control unit is in standby mode and
transmitting the beacon periodically and waiting for commands from the ground station.
5.4
Electrical Power subsystem (EPS):
The satellite's subsystems need to operate at:
•
Two regulated values: 3.3V ± 5% and 5V ± 5%.
•
Unregulated value of 14.4V.
The solar arrays are the main power source and will deliver power during the sunlit part of the
orbit and will cover five faces of the satellite, or two deployed paddles. In eclipse a rechargeable
battery (NiMH cells) will provide power. EPS will exchange data and commands with CDHS
through I2C interface, the data will include voltage, current and temperature measurements,
and commands of switching ON/OFF for EPS will be received from CDHS.
5.5
Structure Design
The launch vehicle is assumed as H-IIA or H-IIB rocket, with payload adaptor PAF239M that
requires the satellite mass to be less than 100 kg. The predicted satellite mass is approximately
30 kg, with a size of 30 cm cubic. An overall view of Otsukimi is shown in Fig. 6.
+X
-X
-Y
+Y
+Z
Figure 6:
-Z
External configuration
4
6.
Orbit/Constellation Description
In order to image the Moon at sunset from the standpoint of a user on the ground at
approximately the sub-satellite point, and to provide the user with a clear image of the Moon
and its phase, the orbit will be a dawn-dusk sun-synchronous orbit, with an inclination of 99.5°.
The orbit selection is motivated by the trade-off between the mission operation mode which
needs relative shadow to get an unsaturated sun light picture of the Moon and the power
generation operation mode. The orbit must also give Otsukimi multiple passes over the Middle
East (Fig. 7). Therefore, Otsukimi will have
the following orbital parameters:
•
Circular Orbit Altitude: 1000 km
•
Angle of Inclination: 99.5 deg
•
Eccentricity: 0 – 0.001
•
Local time at ascending/descending
node: 7:00 p.m. and 7:00 a.m
Figure 7:
7.
Im plem entation Plan
Ground track
2014
Q1
Q2
2015
Q3
Q4
Q1
Q2
Q3
Satellite basic design
Satellite detailed design
Mission e quipment basic design
Mission e quipment detailed design
Mission e quipment prototype
Decide bus component specifications
Thermal structure model production and test
Test mission components developed
Production of mission components test model
Production of FM mission components
Procurement of FM bus components
Satellite FM assembly and test
Launch
Otsukimi will be a low-cost satellite
devleoped in maximum two years
(Fig. 8). The satellite developer
(represented by the Kyushu Institute
of Technology) is well equipped
with infrastructure which will
Figure 8: Project schedule
minimize the cost and hence the risk.
Potential investors and collaborating partners from Arabic countries are private companies or
government agencies from Arabic countries: National Authority for Remote Sensing and Space
Sciences (Egypt) (NARSS), Space Research Institute of Saudi Arabia (KAC ST-SRI), Algerian
Space Agency (ASAL) and SGAC Sudan.
The mission requires the lunar image to identify the phase in the first day of New Moon.
Project and technical risk events include the following:
a.
8.
Single point of failure:
b.
Other risks
1. Mission failure due to ADCS failure
1. Imprecise camera image
2. Mission failure due to Power system fault
2. Radiation damage
3. Mission failure due to Transmission fault
3. Project over budget
References
[1] J. K. Knowles and E. Reissner, Note on stress-strain relations for thin, elastic shells. J. Math. Phys. 37, 269-282 (1958)
[2] H. S. Carslaw and J. C. Jaeger, Operational Methods in Applied Mathematics, 2nd edition. p.121. Oxford University Press, London (1953)
[3] Authors’ Guidelines. Available online at: www.dlr.de/iaa.symp (accessed August 2010)
5
Q4